Embodiments of the invention relate generally to overhead valve (OHV) engines utilizing push rod tubes, and more particularly, to an engine cylinder head and push rod tube configuration.
Overhead valve (OHV) engines use push rods to actuate valves in a cylinder head. The push rods are driven by a camshaft located in the engine block. The push rods actuate one end of a rocker arm which pivots on a trunnion pin or a rocker shaft located above the cylinder head. The other end of the rocker arm actuates an intake or exhaust valve. The rocker assembly is usually encased by a rocker cover.
In some engines, the push rods are contained in push rod tubes which protect the push rods and provide a path for oil to flow between the crankcase and rocker cover. Since push rods typically extend from the cylinder head to the block, when push rod tubes are utilized, they too extend from the cylinder head to the block. This results in requiring an affirmative seal to prevent oil seepage and contamination due to movement and differing expansion and contraction rates. The push rod tubes are therefore either threaded at both ends and screwed into the engine block and the head or the rocker cover, contain o-rings to provide an oil seal, and/or contain annular flanges and gaskets. Unfortunately, these components degrade over time and must be replaced and are time consuming to manufacture and install.
In air cooled internal combustion engines, it may be desirable to position push rod tubes and rocker covers to aid in transferring heat from the cylinder head and block. Air cooled internal combustion engines rely on cooling fins around the periphery of the cylinder block and head to increase surface area over which cooling air flows. However, push rod tubes may become effective cooling devices if they are positioned in the path of cooling air. Also, new enclosure designs for rocker components have the potential to increase surface area available for heat transfer. Rocker covers often act as insulators as they encapsulate the cylinder head, and therefore heat transfer from the cylinder head may be significantly improved with careful design.
Instead of push rod tubes, other engines use push rod passages formed within the cylinder head and block. While push rod passages do not require o-rings and gaskets, they require thicker walls within the cylinder head and block to provide room for the passages and require additional casting or machining steps. The thicker walls increase thermal resistance to heat transfer from the combustion chamber. Push rod tubes formed in the cylinder head also restrict air flow and reduce cooling capacity.
Therefore, it would be desirable to provide push rod tubes without components that degrade over time and that reduce manufacturing and assembly time. It would also be desirable for a cylinder head to have push rod tubes located in a position to maximize heat transfer to the ambient environment and are wholly contained within a single component of the engine. It would be further advantageous if a cylinder head had an enclosure for rocker components that increased heat transfer from the cylinder head.